The present invention relates generally to processes and systems for producing higher molecular weight hydrocarbons from lower molecular weight alkanes, and, in one or more embodiments, to processes and systems that include the conversion of alkyl bromides to higher molecular weight hydrocarbons in circulating catalyst reactor-regenerator systems.
Natural gas, a fossil fuel, is primarily composed of methane and other light alkanes and has been discovered in large quantities throughout the world. When compared to other fossil fuels, natural gas is generally a cleaner but lower-valued energy source. For example, crude oil typically contains impurities, such as heavy metals and high-molecular weight organic sulfides, which are generally not found in natural gas. By way of further example, burning natural gas, or hydrocarbon liquids derived from natural gas, produces far less carbon dioxide than burning coal. However, challenges are associated with the use of natural gas in place of other fossil fuels. Many locations in which natural gas has been discovered are far away from populated regions and, thus, do not have significant pipeline structure and/or market demand for natural gas. Due to the low density of natural gas, the transportation thereof in gaseous form to more populated regions can be expensive. Accordingly, practical and economic limitations exist to the distance over which natural gas may be transported in its gaseous form.
Cryogenic liquefaction of natural gas to form liquefied natural gas (often referred to as “LNG”) is often used to more economically transport natural gas over large distances. However, this LNG process is generally expensive, and there are limited regasification facilities in only a few countries for handling the LNG. Converting natural gas to higher molecular weight hydrocarbons which, due to their higher density and value, are able to be more economically transported as a liquid can significantly expand the market for natural gas, particularly stranded natural gas produced far from populated regions. While a number of processes for the conversion of natural gas to higher molecular weight hydrocarbons have been developed, these processes have not gained widespread industry acceptance due to their limited commercial viability. Typically, these processes suffer from high capital and operating costs and/or relatively low carbon efficiencies that have limited their use.